This invention relates to delivering humidified gas mixtures to be breathed by a patient.
In conventional respirator systems a ventilator draws gases from one or more sources and delivers the gas mixture through inhalation and exhalation conduits to and from the patient in cyclic pulses of about 1 liter volume at a rate of about 6-10 pulses per minute. Conventionally the gas is conditioned, by heating or humidifying or by other treatment, before it is delivered to the patient's breathing passages. For example, a nebulizer may be positioned in the inhalation conduit for adding a medication to the gases. Commonly a humidifier, in which the gas mixture is directed over a reservoir of heated water for warming and adding moisture to the gas mixture, is positioned close to the ventilator and remote from the patient in the inhalation conduit. As the gas mixture flows in pulses from the humidifier, its temperature falls so that the temperature of the gas mixture as it leaves the heater is substantially higher than at the point of delivery to the patient. The extent of such a temperature drop varies according to, for example, the length of the hose carrying the gas to the patient, ambient temperatures, and air movement over the hoses.
Humidifiers in common use typically heat the water over which the air being humidified passes, to about 130.degree.-160.degree. F., and systems using such humidifiers commonly require costly and complex apparatus for feedback control to avoid exposing the patient to gases in excess of body temperature. Maintaining the temperature of the gas at the point of delivery to the patient within a range of safety and comfort requires monitoring, e.g., by placing electronic sensors near the patient, and controlling the humidifier thermostatically.
As the temperature of the gas mixture falls, moisture "rains out" of the gas mixture, condensing on the walls of the conduits. Complete obstruction of the inhalant conduit by condensate can result in drowning the patient. Condensate accumulation is generally greater in the expiratory conduit. A collection device is conventionally provided at a low point in the conduit to drain away and trap accumulating condensate.